Radio transmitting and receiving system



Nov. 30, 1948. I E. LABiN 2,454,810

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RADIO TRANSIITTING AND REOEIVINGSYSTH Filed Jan. 23, 1943 3 Shana-Shut 3 t A A INVENTOR. E M11. E L A E/N Patented Nov. 30, 1948 2,454,810 aamo TRANSMISTT mo AND REcErviN YSTEM Emile Labin, New York, N. Y., assignor to Federal Telephone and Radio Corporation, Newark. N. 3., a corporation of Delaware Application January 23, 1943, Serial No. 473,310

18 Claims. (01. 343-) This invention relates to radio transmitterreceiver systems and more particularly to systems of-the character which operate for brief recurring intervals.

It is customary in radio detection systems and other transmitter and/or receiver systems to use direct current. The supply of direct current for these systems requires considerable equipment in the way of rectifiers, filters, chokes, condensers, etc. Where the systems are to be made portable the equipment for supplying direct current takes up valuable space and adds considerably to the weight of the apparatus.

It is an object of this invention to eliminate much of the bulk, weight and cost of equipment heretofore believed necessary for transmitter and/or receiver systems which operate for brief recurring intervals.

Another object of this invention is to provide a method and means for operating transmitter and/or receiver systems such as radio detection systems directly on an alterat'ing current source in place of the usual source of direct current.

Generally speaking, my invention involves the application of non-rectified, non-filtered, raw alternating current of a given frequency in lieu of direct current, to vacuum tube circuits normally in operation for brief recurring periods. Heretofore, transmitter-receiver systems have depended on vacuum tube circuits having direct current supplied tot he various tube electrodes. I discover that by making modifications in circuit design and/or the inclusion of means to control the alternatingcurrent for the different portions thereof I can use directly a source of alternating current as the power supply for such systems.

The nature (it my invention may be best understood from the following detailed description when read in connection with 'the' accompanying drawings, in which:

Fig. 1 is a block diagram of a radio detection system employing an alternating current source in accordance with this invention;

Figs. 2 and 3 are graphical illustrations showing how alternating current is used in the place of direct current in the system;

Fig. 4 is a schematic wiring diagram of a modulating control circuit;

Fig. 5 is a block diagram of another modulating control circuit; a

Fig. 6 is a schematicillustration of a twostage radio circuit employing stage coupling elements for use with alternating current;

Fig. 7 is a schematic illustration of a two-stage radio circuit in which the design principles of cathode ray oscillograph.

2 I diret current amplifiers are employed with alternating current; and i Fig. 8 is aschematic illustration of a voltage divided circuit supplying the electrodes of the Referring to Fig. 1 of the comprising a pulse transmitter composed of a radio frequency oscillator 8, a pulse modulator 8 and an antenna 10 for transmission of recurring impulses. A receiver Ii and a cathode ray oscillograph l2 are included to receive and indicate echo pulses caused by an obstacle in response to the transmission of impulses. Connecting the output of the pulse modulator 9 to the receiver H is the usual blocking circuit l3 arranged to block the receiver during the transmission of impulses. If desired, the circuit l3 may comprise an R.-C. blocking circuit such as disclosed in my copending application, Serial No. 471.228, filed January 4, 1943.. A sweep generator I4 is also connected to the output of the modulator 9 whereby the sweep A--B of the osciliograph I: is synchronized with the transmission of impulses. Areference pulse control l5,'

apply directly an alternating current source l8.

While this source of current is applied directly to the oscillator 8 and the modulator 9, I preferably pass energy from the same source through a phase control l9 prior to application of the current to the receiver ii, sweep generator M and the oscillograph lg. By controlling the phase of the alternating-current appliedto-the receiver side of the system, a desired portion of a period of the alternating current can be selected for the brief operating period of the receiver means.

Any alternating current source having a frequency such that the interval of receiver operation will cover but a small fraction of the period of the alternating current whereby the amplitude of the current during the interval has negligible percentage variation is satisfactory. That-date,

say, a small percentage variation in thecurreni applied during the operating interval is not ob- Jectional and if the peak portion of the positive drawings, I show, for purposes of illustration, a radio detection system half of a cycle is used this variation may be maintained at a minimum of about one percent. A maximum percent variation up to six or seven percent to both sides of a mean value is not objectionable for most receiver operations. Such point along the positive half of an alternating current cycle. The particular location of the impulse with respect to the alternating current period may be selected as hereinafter more particularly described.

The modulator is arranged to produce and cause transmission of an impulse 20 in the relation shown in Fig. 2. The receiver II will be blocked temporarily by. the device it during transmission of the impulse and thereafter permitted to receive echoes caused by obstacles in response to the transmitted impulse. A desire able range for portable radio detection apparatus may be selected so that the maximum time interval t1 of receiver operation for a given alternating current is about three per cent of a'cycle' thereof and should this operating interval occur for a selected brief period.

'-" tion of the alternating current cycle. This satat the peak portion of the cycle as indicated by the sweep .Al-Bl in Fig. 2 very little variation will occur in the amplitude of thecurrent.

Assuming that the transmitted impulse occurs at 20c on the decreasing portion of the curve,

the interval directly following it Az-Br.wi ll approach a maximum percentage variation.- This' variation can be reduced to a minimum by proper control'of the phase of the alternating current source applied to the receiver side'of the system. By adjusting the phase control I8 an amount 0 the alternating current applied to the receiver side of the system will be retarded in phase so that the peak portion thereof will be used during the receiver operating interval. This interval is indicated by the broken lines asAa-Ba.

The sweep A-B is produced by a saw-tooth wave 2i generated at H in synchronism with the pulse 20 as shown in Fig. 2. When the pulse 20 is varied in position relative to the cycle of-the alternating current as shown at 20a, the saw-.

tooth wave is likewise moved in time as indicated by the broken line curve 2i a.

In Fig. 3, the transmitted impulse "and the sweep Al-Bl is shown at the peak portion of an alternating current. .Should it be desirable to introduce a discard interval is and increase the speed of the sweep for the oscillograph thus magnifying the reception interval ti for Vernier measurement, a discard interval timer 22a may be interposed between the output of the modulator 9 and the sweep generator ll. This interval timer may comprise any suitable adjustable delay device whereby the initiation of a sweep voltage can be delayed a desired time interval.

For radio detection operation, the sweep interval A-B indicates the interval of receiver operation desired. Since the phase of the alternating current source can be controlled by the phase control l9, this brief operating interval can be correlated with the peak portion of the alternating current. The receiver, of course, may be permitted to operate beyond the sweep interval A-B and any reception or interference beyond the sweep interval AB will not appear on the In Fig. 4, I haveshown a form of modulator similar to the direct current-operated modulator disclosed in my copending application, Serial No. 408,499, filed August 12, 1941, which matured into Patent No. 2,408,076. The modulatorcomprises a vacuum tube 22 in which a cathode is selfbiasedto a desired cut-oi! level by a capacity- -resistance circuit 23. The plate circuit of the tube includes an inductance coil 24 and the grid circuitfor the tube is provided with a coil 25 inductively coupled with the coil 24, to provide a positive feedback between the plate circuit and the grid circuit. The alternating currentsource I8 is applied between the cathode circuit and the coil 24. This application of alternating current takes the place of direct current applied in the modulator or pulse generator disclosed in my aforesaid copending application, Serial No. 406,499, now Patent No. 2,408,076. .In operation the plate circuit is adapted to build up to saturation at some point along the ascending porsuch that the discharge of the condenser thereof prolongs the negative charge of the grid of the tube thereby providing an interval between the generation of impulses.

- Besides the form of pulse generator described above other forms of pulse generators such as the a spark type, for example, may be used for modu-.

lating. purposes in r Fig. 1. Should it be desirable to cause generation of the radio detection system an impulse at some point on the descending side or at any other portion of an alternating current wave, a control system such as illustrated in Fig. 5 may be used. This system comprises a clipper 20 adapted to clip the alternating current wave applied thereto from the source l8 substantially as indicated at 21. The resulting wave is substantially rectangular in form and when'applied to a diilerentiating circuit 28 produces alternately positive and negative pulses as indicated at 29. Uni-directional pulses ll may be obtained from the output of the diflerentiating circuit 28 by passing the energy through a threshold device 30 such as a class "C amplifier. The uni-directional pulses 3| may be retarded any desired amount is by passing the pulses through a time delay device 02 and thence to modulator 9. (for example the grid of the tube 22. Fig. 4). this instance tube 22 is biased to such a level that the alternating current will not cause it to operate in the absence of the added pulses. The

energy of these pulses when applied to the grid devices. Also, since this peak portion will vary in potential a very small percent, such variation will halve no adverse effect on the operation of a radio detection system constructed in accordance with my-invention.

A radio detection system intended for use with a source of direct current will require certain alterations before it will satisfactorily operate on alternating current. I have therefore selected certain portions of the system to show specifically the kind of alterations required.

In Fig. 6 I have shown a multi-stage circuit fed by alternating current and designed with the proper time constants to pass high frequencies and'to filter out low frequencies such as the source of alternating current used. .This circuit comprises vacuum tubes 34 and 38 having respectively plates 38 and 40, and 50. Tube 34 has a grid bias resistor 52 in its cathode circuit and the by-pass condenser 54 connected to a common ground 86. Likewise tube 36 has a grid bias resistor 58 in its cathode circuit by-passed by condenser 80 and connected to the common ground 56. The plate supply voltage is. obtained through a transformer 82 fed from the alternating current source it. One end 63 of the secondary is connected through a load resistance M to the plate 38 of tube 35 and also through load resistance 66 to plate M of tube 36. The other end of the secondary is connected to the common ground 56. A grid input resistor 68 is grids t2 and 46, and cathodes 48 F isconnected through resistor 92 to the plate I of tube I8. The cathode It is connected to the slightly above ground potential will be applied thereto. The cathode 86 is connected to a point D on the voltage divider A-F between points B and E. Alternating current voltage is supplied to the voltage divider through a transformer d8 having one end connected to the point P and the other end connected to a ground point 88.

In actual practice, points at which various taps may be made on the voltage divider may be selected so as to provide the necessary operating voltages. The grid bias on tube Iii may be the voltage drop between points A and B. That on tube 18, however, is equal to thediflerence between the voltage which may be developed across a resistance 90 bytthe plate current of tube 10 and the voltage between points D and E. The anode voltage for tube Ill may be equal to that between points B and E less the voltage drop through the resistor an. The anode voltage on tube 18 will be that between points D and F minus the voltage connected to the grid 46 and the other end is connected to a ground point. The two stages are coupled together by a condenser C. The size of condenser C and resistor 88 largely determines the time constants necessary to pass high frequencies and reject the lower frequency of the power used. When properly designed, a circuit as indicated in Fig. 6 may be responsive to signals received when the plates 34 and 36 are positive.

In operation of the multi-stage circuit of Fig. 6 assume that a pulse is applied to the'grid M of tube 3 1 at an instant when the transformer 62 is providing a high positive plate voltage. The .pulse will be amplified by tube and the amplified pulse will beapplied to the grid 46 of the tube 36 and further amplified therein. Ordinarily the application of alternating current may introduce undesired reactions in the grid circuit of tube 38.

However, in accordance with my invention, I

select the condenser C and the resistor 88 to provide a convenient time constant. If the duration of the input pulse is to be 5microsecorlds, for example, I may select a time constant which will allow my circuit to pass any pulsehaving'a duration up to, say of 10 microseconds, and which will offer a high impedance to a pulse lasting several thousand microseconds. Therefore, by proper design it will-be clear that the low frequency supply voltage of the source it introduces negligible re-- actions in the circuit.

In Fig. '2 I have illustrated a known type of multi-stage direct current amplifier wherein no drop through the output resistor 82.

The circuit of Fig. '7 comprises a type of resistance coupling in which the plate of one tube is conductively connected to the control grid of the following tube by a single coupling resistor. The action of this type of directly coupled amplifier depends upon the fact that in any one tube considered by itself, the performance is a result of potential difference between plate and cathode of the first tube and between control grid and cathode in the second tube. This performance is not'afi'ected with reference to ground or with reference to any other tube.

In Fig. 8 I have illustrated a voltage divider H-L having divider connections to cathode ray ably connected to the resistor J. The grid H2 is adjustably connected through a resistor lit to the resistor L. The cathode lid is connected to a point between resistors K and L.

The voltage divider H-L should be arranged either with no by-pass condensers as shown in Fig. 8 or with proportional by-pass condensers around each section thereof so that the time constants of all sections will be substantially alike. The reason for this is because when a blocking condenser is employed between stages modified for operation with an alternating cur rent supply. This circuit comprises a-first vacuum tube 10 having a plate 12, a grid 14 and a cathode it. A second vacuum tube "comprises a plate 80, a grid 82'and a cathode 84. Plate 12 of vacuum tube i0 isdirectly connected to the grid 82 of tube 18. A'coupling resistor 90 has one end connected to the plate I2 of tube ill and the other end connected to a point E about midw'ay on a voltage divider A--F. The point A on the voltage divider A-F is connected to a ground as well as through condenser of more than negligible capacity is connected across one or more sections it may cause an undesirable shift of the phase relations of the various voltages applied to the cathode ray tube.

Although I have described the principles of my invention in connection with specific apparatus, I recognize that many modifications and adaptations thereof are possible. It is to be clearly understood, therefore, that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objectsv of my invention and the appended claims.

. What I claim is:

1. A method of operating .a transmitter-receiver system comprising energizing a transmitter di- 6 a resistor M to the grid ll of tube I0. The point voltage divider A-F at a point B so that avoltage I I 7 teeth! with alternating current. energizing the receiver simultaneously with the energization of the transmitter with the same alternating current and operating the receiver for a period which is a small fraction of the alternating current cycle, whereby only an inconsequential variation in the amplitude of the energizing current will occur during the operation of the receiver.

2. The method defined in claim 1 further including phasing the alternating current applied to the receiver to cause the operating interval of Y the receiver to occur during a portion oi a period thereoi having a minimum of variation in amplitude.

3. The method defined in claim 1 furtherineluding selectively controlling the timing of ,the brief interval of the receiver operation with respect to transmitter operation. Y

4. The method defined in claim 1 wherein the energlzation of the transmitter includes causing comprising simultaneously energizing directly Qwith alternating current all the circuits of the system, and operating the receiver for an interval which is such a small fraction of the alternating current cycle that less than a :7% variation in the mean amplitude of the energizing current will occur during the operating interval 0! the receiver.

6. A method of operating a radio detection system having a transmitter to transmit recurring impulses and a receiver to detect for a brief interval echoes of the transmitted impulses, comprising supplying alternating current directly to the circuits of the system for simultaneous energization thereof, correlating the recurring impulses to occur in a given time relation with .respect to the peak portions of the alternating current, operating the receiver for an interval which is a small fraction ofthe alternating current cycle and controlling the phase of the alternating current applied to the receiver to insure'application thereto of the peak portions thereof during said brief intervals of echo detection.

7. A. method of operating a radio detection system having a transmitter to transmit recurring impulses and a receiver. together with" a cathode ray oscillograph to receive and indicate echoes of the transmitted impulses, which method comprises energizing simultaneously directly the circuits of the system with alternating current, correlating the generation of a sweep potential for the oscillograph to occur in synchronism with the occurrence of said impulses. and causing the peak portions of said current to occur in the circuits oisaid receiver and said oscillographduring the sweep interval of said oscillograph.

8. A method of operating a radio receiver for brief intervals comprising energizing the receiver with alternating current and operating the receiver for a period which is suillciently small to constitute a fraction of the'alternating current cycle to insure an amplitude variation of the I oscillograph. operating the current during such periods of less than 27% o! the mean amplitude of the current.

9. A method defined in claim 8 further including thestep of phasing the alternating current energizing-the receiver to correlate the coincidence of the portionof the, alternating current cycle having a minimum of amplitude variation with the operating interval of the receiver.

10. A method of operating a radio receiver and an oscillograph arrangement for visual indication of signals, received during brief intervals, comprising energizing directly and simultaneously the circuits of the receiver and the oscillograph with alternatin current, deriving sweep potentials from said alternating current for the reeeiver'for a brief periodwhich is recurrent for each alternating current cycle and is such a small fraction thereof that the amplitude variation of the alternating current for the brief interval of receiver operation is less than 27% of the mean amplitude oi the current during such interval, and correlating the occurrence of said sweep potentials with said operating intervals.

'receiver includes means .in th 11. A transmitter-receiver system comprising a transmitter, a receiver. means for applying alternating current to said transmitter and said receiver for the simultaneous energization thereof, and means for operating the receiver at least for an interval whichis such a small fraction of the alternating current cycle as to limit the variation amplitude thereof during such interval to less han :7% of the mean amplitude of the current. g

'12. The system defined in claim 11 wherein the means for supplying alternating current to the receiver means includes means for variably phasing the current to cause the operating interval of the receiver to occur during a portion of the period of the alternating current having a desired'minimum of variation in amplitude.

13. The system defined in claim 11 wherein the transmitter includes means to control the occurrence of impulses with respect to the cycle of the alternating curren.

14. The system defined in claim 11 wherein the providing a time constant between at least certain stages to pass radio frequency energy and to block passage of energy of the alternating current source.

15. In a radio detection system having means to transmit impulses and receiver means to detect and indicate for brief intervals echo pulses caused by obstacles in response to said impulses; the combination therewith of means to supply alternating current directly to the transmitting means-and to the receiver means for simultaneous energization thereof, said current having a frequency to render each cycle thereof large relative to said interval and means for variably phasing the alternating current applied to the receiver means with respect to the application thereof to said transmitting means to insure application to said receiver means of a portion oithe cycle of alternating current having a desired minimum of variation duringsaid brief intervals of detection.

16. In a radiodetection system having means. to transmit impulses and receiver means todetect' receiver means to insure application thereto of a portion of the cycle of alternating current having a minimum of, variation during reception of echo pulses, the receivermeans including a receiver and an oscillograph in combination with means responsive to the transmission of impulses to generate a sweep potential for the oscillograph, and means to retard the timing of the sweep potential with respect to the impulse transmission to provide a discard interval between the occurrence of an impulse and initiation of a.

18. The method described in claim 1 wherein said variation in amplitude is held to be less than 27% of the mean amplitude of the current during said period.

EMILE LABIN.

REFERENCES CITED The following references are of record in the file of this patent:

\ UNITED STATES PATENTE Number Name Date 1,902,235 Heintz Mar. 21, 1933 2,080,081 Loth et a1 May 11, 1937 2,157,312 Wright May 9, 1939. 2,227,598 Lyman et a1. ..J Jan. 7, 1941 FOREIGN PATENTS Number Country Date 302,602 Great Britain May 30, 1929 577,307

France June 3, 1924 

